NEW YORK (CNN/Money) - When you run into car trouble -- and everyone inevitably does -- you're probably hoping the mechanic you chose won't take you for a ride. But since you're not a mechanic, how can you know?

As in any other business, the auto repair industry has honest practitioners and sleazy operators. But, if you use common sense and arm yourself with knowledge, your chances of finding the good ones increase exponentially.

Take a look below at some of the dirty tricks naughty mechanics can pull and tips on how to avoid them.

Evaluate the candidates

Start by using your eyes. Look around the parking lot, said Martin Lawson, executive director of publications for the National Institute of Automotive Service Excellence. If cars being serviced are worth about the same as your own, that's a good sign.

Check to see whether the shop is neat and organized. "Part of professionalism extends to the quality of the shop's appearance," said Ken Roberts, a spokesperson for the Automotive Services Association. It's not going to be hospital clean, Lawson added, but you'll be able to tell whether much attention has been given to upkeep of the facilities.

Look not only for cleanliness but for a courteous staff willing to answer your questions, Roberts added. You don't want to leave the shop feeling like the services you need are still murky, or that anyone has kept information from you.

Look for policies regarding labor rates and any diagnostic fees, Lawson said. If they are not posted, staff should be willing to explain them. And check on the walls for diplomas and credentials, particularly customer service awards. The National Institute for Automotive Service Excellence (ASE) tests automotive technicians. Those who pass receive a certificate they can display on the wall.

"We think it stands to reason that shop owners who encourage technicians to become certified will, as a rule, be equally concerned about other aspects of their work, such as honesty," Lawson said.

You should distrust any shop that won't give you a written estimate prior to any repairs, Roberts said. And if the work that's needed costs more than 10 percent over that estimate, the shop should ask for the consent of the owner before the mechanic starts tinkering with the car.

And stay abreast of common ways a mechanic might swindle you.

Getting a bad brake

"Well, Ma'am, your brakes really could give out at any minute."

Brake shops have more potential for fraud than any other type of shop, according to Mark Eskeldson, author of "What Auto Mechanics Don't Want You To Know". When it comes to car failure, nothing tends to scare people more than the thought not being able to stop -- making it easy for a dishonest mechanic to use scare tactics, cajoling people into paying for an expensive brake job.

Many shops offer free brake inspections, for example. If a mechanic pushes expensive repairs after such an inspection, be wary, particularly if you have your car routinely serviced. The free inspection may just be a scheme to sell you services you may not need.

Beware the low-cost tune-up

The logic behind a low-cost tune-up is that tune-up "specialists", who can do the job faster than ordinary mechanics, charge their customers less for the services. But, Eskeldon cautions people to read the fine print on any ads for dirt-cheap tune-ups. You may not be getting all the services you need.

It may be the only parts installed at that extra-low price are new spark plugs. You need a basic tune-up every 30,000 miles or so -- and that should include both changing the spark plugs and replacing the filters and PCV valve at the very least, Eskeldson said. If the cheap tune-up ad notes "additional parts extra", you may find yourself shelling out for a fuel filter and for the cost of installation. And then your cheap tune-up isn't so cheap anymore.

Trannies

There's no easy way to tell how much an ailing transmission will cost to fix. Your mechanic may not be able to diagnose the problem without a tear-down inspection -- which works like exploratory surgery. But, dishonest mechanics may trap customers into paying for expensive repairs after a tear-down, Eskeldson said. An honest shop will notify you of the labor charge up front, and give you a range of possible total costs before your car is taken apart.